Hydrothermal and Magmatic System of a Volcanic Island Inferred From Magnetotellurics, Seismicity, Self‐potential, and Thermal Image: An Example of Miyakejima (Japan)
Hydrothermal and Magmatic System of a Volcanic Island Inferred From Magnetotellurics, Seismicity, Self‐potential, and Thermal Image: An Example of Miyakejima (Japan)
复制标题
DOI：
10.1029/2021jb022034
复制
发表时间：
2021-06
期刊：
影响因子：
--
通讯作者：
M. Gresse;M. Uyeshima;T. Koyama;H. Hase;K. Aizawa;Y. Yamaya;Y. Morita;D. Weller;T. Rung-Arunwan;T. Kaneko;Y. Sasai;J. Zlotnicki;T. Ishido;H. Ueda;M. Hata
中科院分区：
文献类型：
--
作者：
M. Gresse;M. Uyeshima;T. Koyama;H. Hase;K. Aizawa;Y. Yamaya;Y. Morita;D. Weller;T. Rung-Arunwan;T. Kaneko;Y. Sasai;J. Zlotnicki;T. Ishido;H. Ueda;M. Hata
潜水和岩浆喷发是火山上发生的一些最大的危险。它们是岩石、水和岩浆流体之间复杂的相互作用的结果。理解和评估这些过程仍然是一项具有挑战性的任务，特别是因为通常缺乏对火山建筑物的大规模表征。在这里，我们重点关注三宅岛，这是一座有人居住的 8 公里宽的成层火山，经常发生岩浆活动。我们通过结合四种地球物理技术对其管道系统进行成像：大地电磁、地震活动、自电势和热图像。因此，我们首次在岩石性质、温度、流体含量和流体流动方面对火山岛进行了全面的解释。我们识别出位于粘土盖上方的浅层含水层（深度<1公里），并揭示其与岩浆构造特征和过去喷发活动的关系。在更深的地方（2-4.5公里），我们推断出一个孕震阻力区，被解释为岩浆富气储层（≥370°C）。气体从该储层中通过裂缝管道上升，然后在约 180°C 的温度下释放到延胡索区域。在上升过程中，这些热流体穿过约 1.2 公里长的液体主导区域，导致局部蒸汽爆炸。这种岩浆-热液相互作用阐明了（i）长周期地震事件的起源和（ii）岩浆和热液流体之间的混合机制，这一机制之前在喷气孔的地球化学特征中观察到。我们的结果表明，结合多学科大规模方法是更好地了解火山系统的相关方法，并对监测策略具有影响。
Phreatic and phreatomagmatic eruptions represent some of the greatest hazards occurring on volcanoes. They result from complex interactions at a depth between rock, water, and magmatic fluids. Understanding and assessing such processes remain a challenging task, notably because a large‐scale characterization of volcanic edifices is often lacking. Here we focused on Miyakejima Island, an inhabited 8‐km‐wide stratovolcano with regular phreatomagmatic activity. We imaged its plumbing system through a combination of four geophysical techniques: magnetotellurics, seismicity, self‐potential, and thermal image. We thus propose the first comprehensive interpretation of the volcanic island in terms of rock properties, temperature, fluid content, and fluid flow. We identify a shallow aquifer lying above a clay cap (<1 km depth) and reveal its relation with magmatic‐tectonic features and past eruptive activity. At greater depths (2–4.5 km), we infer a seismogenic resistive region interpreted as a magmatic gas‐rich reservoir (≥370°C). From this reservoir, gases rise through a fractured conduit before being released in the fumarolic area at ∼180°C. During their ascent, these hot fluids cross a ∼1.2‐km‐long liquid‐dominated zone causing local steam explosions. Such magmatic‐hydrothermal interaction elucidates (i) the origin of the long‐period seismic events and (ii) the mixing mechanism between magmatic and hydrothermal fluids, which was previously observed in the geochemical signature of fumaroles. Our results demonstrate that combining multidisciplinary large‐scale methods is a relevant approach to better understand volcanic systems, with implications for monitoring strategies.